The molecular mechanisms that underlie common neurodegenerative diseases remain unclear, although studies have implicated mitochondrial dysfunction and ubiquitin-proteasome defects. The Gunn laboratory studies the RING-type E3 ubiquitin ligase Mahogunin Ring Finger-1 (MGRN1), loss of which causes progressive, widespread spongiform neurodegeneration in mice by 1 year of age. Mitochondrial dysfunction and elevated oxidative stress were detected in the brains of Mgrn1 null mutants by 1 month of age. Mutations in another RING-type E3, Parkin (PARK2), underlie ~50% of inherited and 10-15% of sporadic early-onset Parkinson's disease and cause mitochondrial dysfunction in mice. Recent studies implicate parkin in the autophagic clearance of damaged, depolarized mitochondria. Our preliminary studies indicate that 1) many MGRN1-interacting proteins also associate with parkin or show altered expression in the brains of parkin null mutant mice;2) MGRN1 interacts with several mitochondrial proteins and colocalizes with mitochondria. We hypothesize that MGRN1 is a component of the mitochondrial chaperone system and that loss of MGRN1 function causes mitochondrial dysfunction that triggers parkin-mediated mitophagy. This hypothesis implies a direct connection between ubiquitination and mitochondrial function and represents a novel approach to considering their relationship to neurodegeneration. If MGRN1 has a direct role in mitochondria, future studies could test the effect of different mitochondrial-targeted therapies on the onset and progression of spongiform neurodegeneration in Mgrn1 null mutants and whether loss of MGRN1 function is a susceptibility factor for other neurodegenerative disorders. Aim 1: To test whether there is a genetic interaction between Mgrn1 and parkin. We will test the hypothesis that MGRN1 and parkin have overlapping functions by generating Mgrn1;parkin compound null mutant mice and performing histological and mitochondrial assays to determine whether loss of 1 or 2 functional Mgrn1 alleles alters the CNS phenotype of parkin null mutant mice, and vice versa. Aim 2: To examine whether parkin and MGRN1 have related mitochondrial functions. We will test the hypothesis that MGRN1 is a component of the mitochondrial chaperone system by examining the effect of disrupting MGRN1 on mitochondrial respiration and morphology and determining whether loss of MGRN1 function triggers parkin-mediated mitophagy. We will also examine whether MGRN1 interacts with, ubiquitinates and/or regulates the levels of specific mitochondrial proteins. PUBLIC HEALTH RELEVANCE: Neurodegenerative disorders have a significant impact on affected individuals, their families, the health care system, and society as a whole. They have many potential causes but even when a particular protein has been shown to cause neurodegeneration, exactly how it disrupts neuron function and survival is not well understood. The work outlined in this proposal will help us understand more about the function of a protein called Mahogunin Ring Finger-1 and whether it has similar function(s) in cells as parkin, which is disrupted in some people with inherited forms of Parkinson's disease. We hope that our work will help us understand how these diseases arise and, ultimately, how we can prevent or better treat them.